The present invention relates to an automatic transmission for a vehicle, and more particularly to a transmission which employs a clutch structure containing a power transmission clutch.
This kind of transmissions is arranged to automatically execute clutching operation and shifting operation, which are similar to those executed by a manual transmission, and ensures a high efficiency in power transmission. That is, this kind of the transmissions improves a motive performance and a fuel consumption of a vehicle. Japanese Patent Provisional Publications Nos. H8(1996)-4788, S60(1985)-135336, H6(1994)-221347 and H9(1997)-42387 disclose this kind of transmissions.
For example, Japanese Patent Provisional Publication H8-4788 discloses a transmission in which an outer drive shaft is concentrically disposed around an inner drive shaft and drive gears for respective transmission ratios are disposed around the concentric shafts in series.
However, such a conventional transmission increases its longitudinal dimension according to the increase of the number of transmission ratios. Therefore, if the conventional transmission is adapted to a vehicle equipped with an engine laterally disposed in an engine compartment, the kind of the transmission functions to decrease a longitudinal dimension of a passenger compartment and a space for foots of front seat passengers.
In order to solve the above problems, inventors of the present invention have invented a new type of a transmission in Japanese Patent Application Serial No. H11-280367 which has not been commonly disclosed.
FIG. 4 shows this transmission which comprises a pair of drive shafts 200 and 202 arranged in parallel and a driven shaft 204 in parallel with the drive shafts 200 and 202. Rotational force of an engine is transmitted to the drive shafts 200 and 202 through clutches 206 and 208, respectively. Drive gears 210, 212, 214, 216 and 218 for first to fifth speeds are alternately installed on the drive shafts 200 and 202. Driven gears 220, 222, 224, 225 and 228 corresponding to the drive gears 210, 212, 214, 216 and 218 are fixedly installed on the driven shaft 204. Gear selecting mechanisms for selecting one of the drive gears are installed to the drive shafts 200 and 202, respectively. Thus arranged transmission solves the problems raised in the above-mentioned convention transmission of Japanese Patent Provisional Publication No. H8-4788.
However, this proposed transmission is further required to improve smoothness in shifting operation, more specifically in shifting operations between second and fourth speeds and between third and fifth speeds.
It is therefore an object of the present invention to provide an improved transmission which is capable of suppressing the size of the transmission even if the number of shift positions is increased and which is capable of executing a preferred one-step jump shifting without generating shocks or delay of shifting operation.
A transmission according to the present invention is for a vehicle and comprises a first drive shaft, a first shifting shaft coaxially arranged with the first drive shaft, a first clutch disposed between the first drive shaft and the first shifting shaft. The first clutch is capable of fixedly connecting the first drive shaft and the first shifting shaft. A second drive shaft is disposed in parallel with the first drive shaft. A second shifting shaft is coaxially arranged with the second shifting shaft. A second clutch is disposed between the second drive shaft and the second shifting shaft and is capable of fixedly connecting the second drive shaft and the second shifting shaft. A power transmitting mechanism transmits rotational power from the first drive shaft to the second drive shaft. A plurality of drive gears are disposed on the first and second shifting shafts. An output shaft is arranged parallel with the first and second drive shafts. A plurality of driven gears are fixed to the output shaft and are meshed with the drive gears, respectively. A shifting drive gear is fixed to the first drive shaft. A shifting driven gear is disposed on the output shaft and is meshed with the shifting drive gear. A third clutch is capable of fixedly connecting the shifting driven gear with the output shaft.